my $c = read_your_config_file(); # returns a hash of values
use File::Spec::Functions;
$c->{user} ||= "user";
$c->{admin} || = "admin";
$c->{htmldir} ||= catfile($c->{basedir}, $c->{html});
$c->{userdir} ||= catfile($c->{htmldir}, $c->{user});
$c->{admindir} ||= catfile($c->{htmldir}, $c->{admin});
$c->{email} ||= "$c->{username}\@$c->{domain}";